The fact that a wage gap exists between genders is not up for debate. You already know the all-too-familiar statistic that women earn 77 cents for every dollar that men earn.

But exactly why the gap persists isstill being discussed. A study published in the American Sociological Review offers a new explanation.

Researchers claim that it may be a matter of overtime: Men are more likely than women to put in 50 hours or more of work a week.

As Quartz reports, almost 20% of men worked 50 hours or more per week in 2000—compared with only 7% of women. The study offers a number of explanations for this, including that women are less likely to choose positions that demand long hours and that they are still responsible for the majority of housework and childcare, and therefore can’t work as much overtime.

Unfortunately, those extra hours seem significant: The researchers suggest that the disparity widens the pay gap by 10%. Not only do longer hours often yield more pay, but more of those who work them tend to end up in managerial and professional positions. The reason? Employers are likely to view overtime employees as hard-working, and thus more worthy of climbing the corporate ladder.